The Russian intelligence agencies detained 11 people, including four 'terrorists', who they claimed were 'directly' involved in a terrorist attack on the Crocus City Hall, TASS reported citing Russia's Federal Security Service (FSB) statement on Saturday.

"The activities of intelligence and law enforcement agencies have resulted in the detention of 11 people, including four terrorists, who directly participated in the terrorist attack on the Crocus City Hall," the statement read.

Work is in progress to identify terrorist accomplices and establish all the circumstances of the attack, TASS reported.

The head of the Russian Security Service (FSB), Alexander Bortnikov, has told Ryussian President Vladimir Putin that eleven people have been detained in connection with the attack on the Crocus complex near Moscow on Friday, according to Russian state media.

The Kremlin stated that those detained included "all four terrorists directly involved in the terrorist attack in Crocus," according to TASS and other state media outlets.

Meanwhile, UN Secretary-General Antonio Guterres has also strongly condemned the terrorist attack at Crocus City Hall and has extended condolences to the people and government of the Russian Federation, according to a statement released by Deputy Spokesperson for the Secretary-General Farhan Haq.

"The Secretary-General condemns in the strongest possible terms today's terrorist attack at a concert hall outside Moscow, in which at least 40 people were reportedly killed and over 100 others injured. The Secretary-General conveys his deep condolences to the bereaved families and the people and the Government of the Russian Federation," the statement read.

The Secretary-General also wished a speedy recovery to those injured.

A terrorist attack was carried out at the Crocus City Hall music venue in the city of Krasnogorsk, near Moscow, on Friday (local time) evening.

Unidentified gunmen armed with assault rifles went on a shooting spree. An explosion happened in the building, starting a fire. The special services are conducting a search operation. Moscow Mayor Sergey Sobyanin cancelled all mass events in the capital in the next two days, and a number of other Russian regions followed suit, TASS reported.

On the other hand, the death toll from the attack on the Crocus City complex rose to 93, CNN reported citing the Russian Investigative Committee.

"The death toll will rise further. According to preliminary data, the causes of death were gunshot wounds and poisoning by combustion products," the committee said on Saturday.

"Preliminary results of the inspection of the premises of the concert hall indicate that the terrorists used automatic weapons during the attack, which, along with the ammunition they left behind, were discovered and seized by (investigators)," the committee also said.

"Based on this material evidence, ballistic, genetic and fingerprint examinations are currently being carried out," it added.

"It was also established that the terrorists used a flammable liquid to set fire to the premises of the concert hall."

Earlier Saturday, the governor of the Moscow region, Andrey Vorobyov, said there were still 115 injured people, including five children, in hospitals in Moscow and Moscow Oblast.

The Investigative Committee said inspection of the concert hall was continuing. Emergency services were still clearing the rubble, CCTV footage was being studied and "work has begun with the victims," CNN reported.